Philips introduced the compact audio cassette medium for audio storage in Europe in 1963, and in the United States in 1964, under the trademark name Compact Cassette. Although there were other magnetic tape cartridge systems, the Compact Cassette became dominant as a result of Philips's decision in the face of pressure from Sony to license the format free. It went on to become a popular (and re-recordable) alternative to the 12 inch vinyl LP during the late 1970s. Compact Cassettes consist of two miniature spools, between which a magnetically coated plastic tape is passed and wound. These spools and their attendant parts are held inside a protective plastic shell.
Two stereo pairs of tracks (four total) or two monaural audio tracks are available on the tape; one stereo pair or one monophonic track is played or recorded when the tape is moving in one direction and the second pair when moving in the other direction. This reversal is achieved either by manually flipping the cassette or by having the machine itself change the direction of tape movement ("auto-reverse"). Tape cassettes were produced in various lengths to a maximum of 2 hours (1 hour each side of a C120 cassette).
A Microcassette (often written generically as microcassette) is an audio storage medium introduced by Olympus in 1969. It uses the same width of magnetic tape as the Compact Cassette but in a much smaller container. By using thinner tape and half or a quarter the tape speed, microcassettes can offer comparable recording time to the compact cassette. The original standard microcassette, the MC60, gives 30 minutes recording per side at its standard speed of 2.4 cm/s, and double that duration at 1.2 cm/s; an MC90, giving 45 minutes per side @ 2.4 cm/s, is also available from a few manufacturers.
Unlike the Compact Cassette, a choice of recording speeds was provided on the original recorders and many others; the tape also spools in the opposite direction, from right to left. For transcription purposes, continuously variable speed was provided on many players. Microcassettes have mostly been used for recording voice. In particular, they are commonly used in dictation machines and answering machines.
The Mini Cassette, often written minicassette, is a tape cassette format introduced by Philips in 1967. It is used primarily in dictation machines and was also employed as a data storage for the Philips P2000 home computer. Unlike the Compact Cassette, also designed by Philips, and the later Microcassette, introduced by Olympus, the minicassette does not use a capstan drive system; instead, the tape is propelled past the tape head by the reels. This is mechanically simple and allows the cassette to be made smaller, but produces a system unsuited to any task other than voice recording, as the tape speed is not constant (averaging 2.4 cm/s) and prone to wow and flutter.
However, the lack of a capstan means that the tape is well suited to being repeatedly rewound and fast-forwarded short distances, leading to the minicassette's continuing use in the niche markets of dictation and transcription, where fidelity is not critical, but robustness of storage is, and where analog media are still widely preferred.